contracts-bedrock: fix invariant test

New version of forge is more strict in how it does invariant testing,
need to specify the ABI using a special `targetInterfaces` function.

https://github.com/foundry-rs/foundry/pull/5605

h/t msolomon

packages/contracts-bedrock/test/invariants/SystemConfig.t.sol

@@ -8,6 +8,11 @@ import { ResourceMetering } from "../../src/L1/ResourceMetering.sol";
 import { Constants } from "../../src/libraries/Constants.sol";
 
 contract SystemConfig_GasLimitLowerBound_Invariant is Test {
+    struct FuzzInterface {
+        address target;
+        string[] artifacts;
+    }
+
     SystemConfig public config;
 
     function setUp() external {
@@ -56,6 +61,19 @@ contract SystemConfig_GasLimitLowerBound_Invariant is Test {
         targetSelector(selector);
     }
 
+    /// @dev Allows the SystemConfig contract to be the target of the invariant test
+    ///      when it is behind a proxy. Foundry calls this function under the hood to
+    ///      know the ABI to use when calling the target contract.
+    function targetInterfaces() public view returns (FuzzInterface[] memory) {
+        require(address(config) != address(0), "SystemConfig not initialized");
+
+        FuzzInterface[] memory targets = new FuzzInterface[](1);
+        string[] memory artifacts = new string[](1);
+        artifacts[0] = "SystemConfig";
+        targets[0] = FuzzInterface(address(config), artifacts);
+        return targets;
+    }
+
     /// @custom:invariant The gas limit of the `SystemConfig` contract can never be lower
     ///                   than the hard-coded lower bound.
     function invariant_gasLimitLowerBound() external {